March 04, 2010

Ancient mtDNA from the US Southwest

Journal of Archaeological Science doi:10.1016/j.jas.2010.01.024

Ancestral Puebloan mtDNA in context of the greater southwest

Meradeth H. Snowa et al.

Abstract

Ancient DNA (aDNA) was extracted from the human remains of seventy-three individuals from the Tommy and Mine Canyon sites (dated to PI-II and PIII, respectively), located on the B-Square Ranch in the Middle San Juan region of New Mexico. The mitochondrial DNA (mtDNA) haplogroups of 48 (65.7%) of these samples were identified, and their frequency distributions were compared with those of other prehistoric and modern populations from the Greater Southwest and Mexico. The haplogroup frequency distributions for the two sites were statistically significantly different from each other, with the Mine Canyon site exhibiting an unusually high frequency of haplogroup A for a Southwestern population, indicating the possible influence of migration or other evolutionary forces. However, both sites exhibited a relatively high frequency of haplogroup B, typical of Southwestern populations, suggesting continuity in the Southwest, as has been hypothesized by others ([Carlyle, 2003], [Carlyle et al., 2000], [Kemp, 2006], [Malhi et al., 2003] and [Smith et al., 2000]). The first hypervariable region of twenty-three individuals (31.5%) was also sequenced to confirm haplogroup assignments and compared with other sequences from the region. This comparison further strengthens the argument for population continuity in the Southwest without a detectable influence from Mesoamerica.

10 comments:

The recent study by Sandoval, which tested 500 Mexican Indians, found mtdna C at a high rate twice in 2 northwestern Mexican people, the Pima and the Tarahumara. This study says southwestern USA ancient mtdna was predominantly B, and that these results are in line with previous studies of living southwestern USA Indians, which also found high rates of mtdna B. This would indicate 2 mtdna "zones" in the great desert region of western North America. But I wasn't able to find samples of southwestern USA Indians who were predominantly mtdna B. I found 48 Navajos who had 18 B samples, and 25 Apaches who had 4 B samples, for a total rate of 30% mtdna B. This is similar to the 20% mtdna B in central Mexico. Maybe I've missed some other study of southwestern USA Indians that found high amounts of B.

The study says these results don't support a demic diffusion from Central America, where the agricultural revolution started. The corn of the USA Indians came from south Mexico, where it was first domesticated 10,000 years ago.

I had also observed, just last month, that there's a sharp mtdna separation between Bolivian highland people, typically Aymara and Quechua, who are mostly mtdna B, and eastern Bolivian Indians, who instead have the typical South American 4-way combination of A, B, C, D. Eastern Bolivia is known for being a long-lived agricultural region, probably going back thousands of years. The agricultural revolution in South America started in the Peruvian/Bolivian region. Seems like once again the diffusion of agriculture did not involve mass migration of people.

I looked at mitosearch samples from southwestern USA (California, Arizona, New Mexico) and from Mexico. ABCD samples were 94 and 238, respectively. Southwestern USA had 25% A, 45% B, 25% C. Mexico had 40% A, 25% B, 25% C. That certainly confirms the study's claims that southwestern USA has a high rate of B.

And this makes Sandoval's recent study of northwestern Mexico very interesting, because like I said, he found instead high rates of C, twice, in people from different states (Sonora and Chihuahua). He found 11/15 and 83/93, or 75% and 90% mtdna C. The 2 populations are separated by 400 km.

It looks like evidence of a remarkably well preserved mtdna structure in the deserts of western North America.

Unlike the Pueblo, Navajo and Apache are not originally SW. They are recent newcomers to the region. That should explain the above-noted discrepancy.

Wikipedia isn't always correct, but confirms this:

Archaeological and historical evidence suggests that the Athabaskan ancestors of the Navajo and Apache entered the Southwest after 1000 AD, with substantial population increases occurring in the 13th century. Navajo oral traditions are said to retain references of this migration.

"Unlike the Pueblo, Navajo and Apache are not originally SW. They are recent newcomers to the region. That should explain the above-noted discrepancy."

Here is an interesting paper (full text available) which suggests that the Navajo and Apache have significant presence of haplogroups B and C:

Gene flow across linguistic boundaries in Native North American populations:http://www.pnas.org/content/102/5/1312.long

I believe that some of the conclusions of the paper have been challenged, such as the assertion that there were three migrations into the Americas, but it does do a nice job of illustrating mtdna distributions in some Western North American native groups.

(Also, the Haida language is no longer believed to be in the Na-Dene group. However, that doesn't signficantly influence the result of the paper.)

Apaches and Navajos are matrilineal and matrilocal. Matrilocality is strongly correlated on a worldwide scale with migration, as males in a migrating population prefer their wives to stay with the wife's parents. The practice of matrilocality would prevent mtDNA haplogroups B and C from entering the migrant population such as the Apache-Navajo from the Pueblo populations that it encountered as a result of the migration.

The pattern of absorption of the maternally-transmitted lineages into the Apache and the Navajos is appropriate for patrilocality. But in general patrilocality is not typical for Na-Dene Indians. It's possible that the Apaches and the Navajos settled in the Southwest in a very distant past (archaeology can't really ascertain their antiquity as material culture may change without populations moving in or out) and went through periods of patrilocality and matrilocality. Alternatively they may have had haplogroups B and C with them all along.

"Anthropologists agree that circa anno Domini 1400 the ancestors of Navajos and Apaches migrated from the Mackenzie Basin of Canada to the Southwest region, where they came into contact with Amerind-speaking populations who had been living there for thousands of years (31). "

This seems to be in conflict with the idea that the Navajo and Apache migrated to their current location in the "very distant past."

Also, there are many native people in North America who practised matrilocality, to some degree:

Hurons, Slave, Cree and many other native groups have been documented to excercise matrilocality, not just the Apache and Navajo.

"Interestingly, the pattern of genetic exchange is not reciprocal. A-group haplotypes would have appeared in the Pima sample if they had absorbed a substantial number of Athabascan-speaking migrants. The pattern of asymmetrical genetic exchanges is all the more interesting given current mate exchange practices. Today, marriage practice in both the Western Apache and Navajo is strongly matrilineal. On this basis, we would not expect to see the inclusion of female lineages introduced from the surrounding non-Athabascan-speaking populations. However, the practice of matrilineality in these populations is likely to have begun after the Navajos and Apaches arrived in the Southwest (31). This practice makes it likely that the haplogroup B and C mtDNA sequences carried in the Navajo and Apache today were introduced early in their experience in the Southwest, and before the current cultural practices were initiated. "

So, although the Apache and Navajo practised matrilocality, it seems that they weren't rigid about.

"'Anthropologists agree that circa anno Domini 1400 the ancestors of Navajos and Apaches migrated from the Mackenzie Basin of Canada to the Southwest region, where they came into contact with Amerind-speaking populations who had been living there for thousands of years (31).'

This seems to be in conflict with the idea that the Navajo and Apache migrated to their current location in the "very distant past.""

On the uncertainties with the timing of the emergence of Athabascan-speakers in the Southwest, see Seymour, 2009 Comments on Genetic Data Relating to Athapaskan Migrations: Implications of the Malhi et al. Study For The Apache and Navajo. American Journal of Physical Anthropology 139(3):281-283.

I brought new data to bear on the problem of timing and origins of the Navajo and Apaches in Dziebel, The genius of kinship: the phenomenon of human kinship and the global diversity of kinship terminologies (2007). As an anthropologist, I'm not one hundred percent satisfied with the dominant interpretation of when and how the Apaches and the Navajos got to the Southwest.

So, the presence of mtDNA B and C haplotypes in Southern Athabascans could represent a relic of Na-Dene heritage largely lost from Northern Athabascans. Alternatively, it's indeed possible that they haven't followed matrilocality stringently. In this case, it looks like they veered away from the norm quite a bit as the admixture is pretty substantial.

True, SW NaDene are closely related to Athapaskans in Canada. And true, there seems to have been a recent (post-1000bp) southward wave of subarctic hunters (Arctic longbow, etc.).

HOWEVER, the archaeological evidence over thousands of years seems to indicate populations in Yukon were founded from the south, i.e. up the Rocky Mountain chain.

Therefore, Athapaskans could have a very ancient southwestern ancestry afterall!

One more thing to consider: If Athapaskans came to America in a more recent migration--later than the rest of Amerinds--wouldn't you expect to find, say, Chukchi DNA among them? (like the recent find in Greenland)

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